Fuels for reaction motors



FUELS FOR REACTION MOTORS John L. Van Winkle, San Lorenzo, and FrancisG. E0110 and Rupert C. Morris, Berkeley, Calif., assignors to ShellDevelopmentCompany, New York, N.Y., a corporation of Delaware NoDrawing. Application December 31, 1956 Serial No. 632,626 a Claims. (Cl.60-3s.4)

This invention relates to liquid propellants for reaction propulsiondevices, particularly to self-sufiicient liquid propellants for rocketmotors. The invention provides a new class of fuels for use inrocketmotors, these new fuels being characterized by their outstandingignition and burning characteristics with standard oxidizing agents. Theprovision of suitable propellants and/ or ignition systems forreaction-type motors, that is, motors which directly apply Newtons thirdlaw of motion, such as rocket or jet motors, presents many interrelatedproblems. For example, it is usually necessary that the propellant beself-suflicient, in the sense that it must contain all of the materialsnecessary to its combustion and must operate without reliance on anymaterial coming from without the propelled object. This problem has beensolved to some extent by the use of so-called monofuels, by which ismeant fuels which contain in and of themselves of low corrosivity andgood compatibility with ordinary materials of construction; (g) stablechemically, inert with respect to ordinary materials of construction,and insensitive to thermal or mechanical shock; (h) easily andinexpensively derived from available raw materials and (1') having ahigh specific thrust.

At the present time,'few compounds have been dis covered whichfulfilsatisfactorily all of these require: ments. Applicants, however,have found a class of materials which substantially comply with all ofthese requirements for a satisfactory liquid rocket fuel, said materialsall of the components essential to the combustion of the fuel. Suchpropellants can be ignited, and flame-outs prevented only through theuse of a separate ignition system. Such ignition systems generally takeone of two forms: a mechanical or electrical ignition system, or ahypergolic ignitor. A hypergolic igniter is a material whichspontaneously ignites, and may be a single material which. spontaneouslyignited when introduced into the propellant composition, or it maycomprise two or more materials which spontaneously ignite when mixed,

normally in the combustion chamber. In either form of ignition system,the system represents. dead weight which also must be propelled by thepropellant.

I As an alternative to the monofuel system, there has been used themulti-component propellant wherein one or more fuels are mixed with oneor more oxidizers in I the combustion chamber, the respective componentsof the propellant being so chosen that the mixture thereof ishypergolic-that is, the two materials ignite spontaneously when mixed.In such a system, ignition of the propellant is accomplished in a simplemanner without any external means and flameouts are substantiallyprecluded.

Also, in many applications, it is mandatory that the reaction-motordevelop its maximum thrust in as short a having excellent.hypergolicity-stability characteristics with respect to ordinaryoxidizing agents.

The terms fuel and oxidizer or oxidizing agent, as used herein, havetheir ordinary meanings-Le, a fuel is a material oxidized or burned; anoxidizer or oxidizing agent is the material which causes, effects andsupports the oxidation or burning of the fuel. I

The new class of rocket fuels discovered by applicants comprises atleast one phospholane or phosphorinane in which the phosphorus atom isdirectly attached to the nitrogen atom of an amino group. Thesecompounds may also be characterized as the cyclic amides of glycoldiesters of phosphorous acid; they have the structural formula:

wherein X represents a chalcogen element and R represents the residue ofa dihydric aliphatic alcohol, HOROI-I, wherein the hydroxyl groups aresubstituted on difierent carbon atoms separated from each other by notmore than one intervening carbon atom, and n represents l, 2 or 3. Inthe preferred compounds of this class, X represents an oxygen or sulfuratom, and R is a divalent saturated hydrocarbon radical, even morepreferably an alkylene radical, the atoms designated as X being linkedto different carbon atoms of the said alkylene radical, the two carbonatoms so linked being separated by up to one intervening carbon atom. Inphospholanes of this class, the carbon atoms of the group R linked tothe atoms designated as X are adjacent carbon atoms; in thephosphorinanes of this class,'the carbon atoms linked to the atomsdesignated as X are separated by one carbon atom. The vale'nces of thecarbon atoms of the group R not linked to other atoms of the phospholaneand phosphorinane rings are satisfied by either hydrogen atoms, or bylinks to carbon atoms of hydrocarbon groups, preferably alkyl groups,and still more preferably lower alkyl groups, such as those containingnot time as possible after the motor is started. Highly hypergolicpropellant mixtures are of substantial advantage in this type ofapplication.

7 Consequently, there is much interest in the discovery and developmentof materials which are highly hypergolic with respect to materialscommonly used as oxidizing agents, yet which are not explosivethemselves, and which do not form explosive mixtures with the oxidizingagent employed. In addition, the fuel must meet the other requirementsfor satisfactory rocket motor fuels, such as: (a) low freezing point,and low viscosity near the freezing point; (b) high boilingpoint and lowvapor pressure at ordinary or moderately elevated temperatures F.); (c)low toxicity; (d) high energy content per unit weight-high density andheat of combustion; (e)

"yielding oxidation products of low molecular weight; (f) 7 more than 4carbon atoms in each group.

The novel compounds of this invention may also be characterized by theformula:

wherein X, R and n have the meanings hereinbefore set out, R has themeaning set out hereinafter and m=3n. ,In the formula amino representsan amino radical, that is, the residue of ammonia or an organic amine,and can be represented by the general formula --N(R') wherein R isselected from the group consisting of the hydrogen atom and organicradicals, and wherein both groups R together can represent a divalentradical which forms with the nitrogen atom a heterocyclic ring. Theamino group preferably is the residue of an amine hav-v ing attached tothe nitrogen atom from one to two hydrocarbon groups. Preferably thehydrocarbon groups are aliphatic groups such as alkyl groups, andpreferably are lower alkyl, including cycloalkyl, groups containing notmore than 6 carbon atoms each, or where both of R together represent asingle group, they represent an alkylene group, preferably onecontaining not more than 10 carbon atoms.

Representative examples of this class of fuels include the following:

The structure of these compounds is illustrated by the followingexamples:

2-dimethy1amino-4-methyl-l,3,2-dioxaphosph0lane2-pyrrolidyl-4,5-dimethyl-1,3,2-dioxaphosphorinane2-butylamino-l,3,2dithiaphospholane can s-cHl N-ethylbis(2-(1,3;2-dioxaphospholanymamine The new fuels are easily prepared bymethods known in the art, the most convenient method being that set outby Lucas, Mitchell and Scully, Journal of the American Chemical Society,72, 5491 1950 This method employs readily available, inexpensive rawmaterialsi.e., glycols, phosphorus trichloride and primary or secondaryamines. According to this method, the glycol is added to a solution ofthe phosphorus trichloride in an inert solvent, such as a liquid alkaneor halogenated alkane, pentane, chloroform or methylene chloride beingquite suitable, the temperature of the mixture being maintained so thatgentle boiling of the mixture and evolution of hydrogen halide occur.When evolution of the hydrogen halide ceases, the mixture is reactedwith an excess of the amine. In some cases, it is desirable to removethe solvent and any unreacted glycol after the reaction is complete, andthen react the 2-chlorophos pholane or phosphorinane with the amine,preferably in an inert solvent.

These new rocket fuels are highly hypergolic, but not explosive, withrespect to materials commonly used as oxidizers for liquid rocket motorpropellants, such as red fuming nitric acid, white fuming nitric acid,mixed acid (nitric acid with a small percentage of sulfurc acid),hydrogen peroxide or liquid oxygen. These new fuels may be used in anyrocket, jet or other reaction motor, designed to operate onfuel-oxidizer propellants. This type of reaction motor, the method ofhandling the fuel and oxidizer and of conducting the combustion are wellknown in the art; for these purposes, the new fuels are substantiallyequivalent to other known fuels. Current practice with respect to theuse of hypergolic fuel-oxidizer propellants is illustrated in somedetail in U.S. Patent No. 2,573,471. It should be remembered, however,that the new fuels ignite spontaneously at an extremely high rate ofspeed when contacted with the oxidizing agent,

, ignition delays being of the order of 50 milliseconds or less. Maximumthrust is developed in an exceedingly short time. Accordingly,precautions should be taken to insure that premature contact of the fuelwith the oxidizer does not occur.

The individual Z-amino-1,3,2-dioxaphospholanes and phosphorinanes may beused asthe fuel, or mixtures of these compounds may be used. In manycases, mixtures have substantial advantages over the individualcomponents thereof used each alone, for such mixtures often have moredesirable physical characteristics than those below about --54 C.

of any of the individual components thereof. For example, mixtures ofclose homologs or analogs of this class of compounds normally have lowerfreezing points than do'any of the component compounds of the mixture,the mixture thus being useful at temperature conditions where none. ofthe component compounds thereof can be used. The most desirable of thesemixtures are, of course, the eutectic mixtures. Asan illustration of theuse of mixtures, rather than the individual compounds of this invention,it has been found that the utility of 2-dimethyl-amino-4-methyl-l,3,2-dioxaphospholane, one of the mostpromising compounds of this invention, could be extended substantiallyby mixing it with its homolog, 2-dimethylamino-1,3,2-dioxaphospholane.The 4-methyl derivative alone has a freezing point of about -47 C.- thefreezing point of the analog is about 30 C.; mixtures of these twocompounds freeze at much lower temperatures, such mixtures containingfrom about 20% to about 60% by weight of the 4-methyl derivativefreezing F.). The eutectic mixture, about 55% by weight of the 4-methylderivative, freezes at about 59 C., a temperature which represents asubstantial extension in the utility of the two component compounds.

The utility of the Z-amino-l,3,2-dioxaphospholanes, -phosphorinan,es andtheir thia analogs as highly hypergolic fuels when used with standardoxidizing agents is shown by the following tables, which summarize theresults of ignition tests of representative members of these newcompounds with several of the standard oxidizers. The method used fordeterminingthe ignition delay comprises injecting a measured amount ofthe oxidizer into a measured amount of the fuel under controlledtemperature conditions. The time between injection of the oxidizer andcombustion of the mixture is measured both photoelectrically andphotographically. The ignition delay is reported in milliseconds.

Table I [Oxidizerz 100% white fuming nitric acid.]

Table II [Oxidizerz 90% white fuming nitric acid. Fuel:Z-dimethylamino-4-methy1-1,3,2-dioxaphospholane.]

Temperature, C.: Ignition delay (milliseconds) 20 Table III [Oirldlzerz90% hydrogen peroxide. Fuel: 2-dimethylamino-4methyl-1,3,2-dioxaphospholane.]

Temperature, C.: Ignitiomdelay (milliseconds) 20 16 19 Table IV[Oxidizem 100% red fuming igtlric acid. Temperature:

Fuel: Ignition delay (milliseconds) 2 dimethylamino 4 methyl -1,3,2dioxaphospholane 20 Eutectic (for composition see Table I) 19 It shouldbe noted that-while the new amino-phospholanes and phosphorinanes areprimarily useful as fuels for reaction motors, they also are useful ascomponents for hypergolic igniter mixtures for other fuels, or ascomponents for more complex fuel compositions for applications whereinit is desirable that high-speed, highintensity combustion be attainedand/or maintained.

We claim as our invention:

1. In the method for developing thrust in a jet motor having acombustion chamber and an exhaust nozzle wherein an oxidizer and a fuelare brought together in the said combustion chamber and the gaseousproducts produced by combustion of the oxidizer and fuel are ejectedfrom the exhaust nozzle, the improvement comprising bringing together anoxidizer and at least one compound of the formula:

wherein X represents a member of the group consisting of oxygen andsulfur, R represents an alkylene group of up to 27 carbon atoms, theatoms designated as X each being linked to different carbon atoms of thesaid alkylene group, the two carbon atoms of the alkylene group solinked being separated by not more than one intervening carbon atom, Rrepresents a member of the group consisting of the hydrogen atom andlower alkyl, including cycloalkyl, groups, with the proviso that both ofthe groups, R, together can represent a lower alkylene group formingtogether with the indicated nitrogen atom a heterocyclic ring, nrepresents an integer from 1 to 3 and m- 3n the ratio of compound ofsaid formula to oxidizer being? in such proportions as to producespontaneous ignition.

2. Inlthe method for developing thrust in a jet motor having acombustion chamber and an exhaust nozzle whereinan oxidizer and a fuelare brought together in the said combustion chamber and the gaseousproducts produced by combustion of the oxidizer and fuel are ejectedfrom the exhaust nozzle, the improvement comprising using as the fuel atleast one 2-amino-1,3,2- dioxaphospholane the ratio of fuel to oxidizerbeing in such proportions as to produce spontaneous ignition.

3. In the method for developing thrust in a jet motor having acombustion chamber and an exhaust nozzle wherein an oxidizer and a fuelare brought together in the said combustion chamber and the gaseousproducts produced by combustion of the oxidizer and fuel are ejectedfrom the exhaust nozzle, the improvement comprising using as the fuel atleast one 2-amino-1,3,2- dioxaphosphorinane the ratio of fuel tooxidizer being in such proportions as to produce spontaneous ignition.

4. In the method for developing thrust in a jet motor having acombustion chamber and an exhaust nozzle wherein an oxidizer and a fuelare brought together in the said combustion chamber and the gaseousproducts produced by combustion of the oxidizer and fuel are ejectedfrom the exhaust nozzle, the improvement comprising using as the fuel atleast one amide of a primary amine and a2-hydroxy-1,3,2-dioxaphospholane the ratio of fuel to oxidizer being insuch proportions as to produce spontaneous ignition.

5. In the method for developing thrust in a jet motor having acombustion chamber and an exhaust nozzle wherein an oxidizer and a fuelare brought together in the said combustion chamber and the gaseousproducts produced by combustion of the oxidizer and fuel are ejectedfrom the exhaust nozzle, the improvement comprising using as the fuel atleast one amide of a secondary amine and aZ-hydroxy-l,3,2-dioxaphospholane the ratio of fuel to oxidizer being insuch proportions as to produce spontaneous ignition.

6. In the method for developing thrust in a jet motor having acombustion chamber and an exhaust nozzle wherein an oxidizer and a fuelare brought together in the said combustion chamber and the gaseousproducts produced by combustion of the oxidizes and fuel are ejectedfrom the exhaust nozzle, the improvement comprising using as the fuel2-dimethylamino-4-methyl- 1,3,2-dioxaphospholane the ratio of fuel tooxidizer being in such proportions. as to produce spontaneous ignition.

7. In the method for developing thrust in a jet motor having acombustion chamber and an exhaust nozzle wherein an oxidizer and a fuelare brought together in the said combustion chamber and the gaseousproducts produced by combustion of the oxidizer and fuel are ejectedfrom the exhaust nozzle, the improvement comprising using as the fuel amixture comprising from about 20% by weight to about 60% by weight ofZ-dimethylamino-4-methyl-1,3,2-dioxaphospholane, the remainder of saidmixture being Z-dirnethylamino-1,3,2-dioxaphospholane the ratio of fuelto oxidizer being in such proportions as to produce spontaneousignition.

8. In the method for developing thrust in a jet motor having acombustion chamber and an exhaust nozzle wherein an oxidizer and a fuelare brought together in the said combustion chamber and the gaseousproducts produced by combustion of the oxidizer and fuel are ejectedfrom the exhaust nozzle, the improvement comprising using as the fuel amixture consisting of 55% by Weight of2-dimethylamino-4-methyl-l,3,2-dioxaphos pholane and 45% by weight of2-dimethylamino-1,3,2- dioxaphospholane the ratio of fuel to oxidizerbeing in such proportions as to produce spontaneous ignition.

9. A mixture comprising from about 20% by weight to about 60% by weightof 2-dimethylamino-4-rnethyl- 7 1,3,2-di0xaphospholame and from about80% by weight to about 40% by weight of l 2-dimethyIamino.-1;3,2-dioxaphospholane freezing. below about --.54'C.

10. The eutectic mixtureeonsisting of about 55% by weight ofZ-dimethylamino4 -methyl 11,3 2- dioxaphospholane and about 45% .byweight of Z-dimethylamino- 1,3,2-dioxaphospholane \freezing at about 59C.

References Cited "in-the file of this patent UNITED STATES PATENTS Lucasat 211.:

Van Winkle et a1 June 28, 1955 OTHER REFERENCES JACS, 72 1952 5491-5491

1. IN THE METHOD FOR DEVELOPING THRUST IN A JET MOTOR HAVING A COMBUSTION CHAMBER AND AN EXHAUST NOZZLE WHEREIN AN OXIDIZER AND A FUEL ARE BROUGHT TOGETHER IN THE SAID COMBUSTION CHAMBER AND THE GASEOUS PRODUCTS PRODUCED BY COMBUSTION OF THE OXIDIZER AND FUEL ARE EJECTED FROM THE EXHAUST NOZZLE, THE IMPROVEMENT COMPRISING BRINGING TOGETHER AN OXIDIZER AND AT LEAST ONE COMPOUND OF THE FORMULA: 